This invention relates to a process for alkylating an alkylatable isoparaffinic hydrocarbon with olefinic hydrocarbons. More specifically, this invention relates to a process for producing an alkylation reaction product from an isoparaffinic reactant, a lighter olefinic reactant and a heavier olefinic reactant, utilizing acid-acting alkylation catalysts. This invention further relates to the process for producing an alkylation reaction product having superior qualities as a component of motor fuels, in comparison to the product produced by previously employed alkylation processes.
Alkylation of isoparaffinic hydrocarbons, such as isobutane, isopentane and the like, with olefinic hydrocarbons such as propylene, butylenes, amylenes, and the like, is well known as a commercially important method for producing gasoline boiling range hydrocarbons. The C.sub.5 --C.sub.10 hydrocarbons generally produced by the alkylation reaction are termed "alkylate." Alkylate is particularly useful as a motor fuel blending stock because of its high motor octane and research octane ratings, such that it can be used to improve the overall octane ratings of gasolines to comply with the requirements of modern automobile motors. Such high octane products are particularly important in producing unleaded motor fuels of sufficient quality when it is desired not to employ alkyl lead compounds in the fuel to meet octane requirements. A continuing goal of the art is to provide an isoparaffin-olefin alkylation process which produces an alkylate product having higher motor and research octane ratings than is possible using conventional processes.
Recent trends in motor fuel requirements and projections of future requirements in this area indicate that the production of motor fuels distilling at end points below about 300.degree. F. may be desirable and/or necessary to meet projected standards. Conventional isoparaffin-olefin alkylation processes do not have the capacity to produce an alkylate product having a distillation end point low enough to be useful in providing such low end point motor fuels. The process of the present invention provides a method whereby an alkylate product having a significantly lower distillation end point than possible using conventional processes may be produced, in addition to the increased value of the product of the present process resulting from octane rating improvements.
In general, commercial isoparaffin-olefin alkylation processes employ isobutane as the isoparaffin and propylene and/or butylenes as the olefins. Catalysts utilized include hydrogen fluoride, sulfuric acid and other like acidic or acid-acting materials. The isoparaffin, olefins and catalyst are typically contacted in an alkylation reactor, forming a reaction mixture. After the alkylation reaction is substantially complete, the reaction mixture is withdrawn from the reactor and is separated into hydrocarbon and catalyst phases in a separation zone, generally by settling in a settling vessel, and the catalyst thus separated is recycled to the reactor for further use. The hydrocarbon phase produced is further processed, for example, by fractionation, to recover the alkylate product and to separate unconsumed reactants, e.g., isoparaffin, for further use.
It has been found preferable to conduct isoparaffin-olefin alkylation processes at particular conditions of temperature and pressure, and at specific concentrations of reactants and catalysts in order to produce an optimum yield of high quality alkylate product. A large molar excess of isoparaffin, relative to olefin, in the reaction mixture, generally about 10:1 to about 30:1, is one of the conditions required to provide even an adequate product. It has been found desirable to employ as large an excess of isoparaffin as possible, since the quality of the alkylate product is improved thereby. Thus, a considerable amount of isoparaffin is generally recovered and recycled to the reactor after separation from the hydrocarbon phase of the reactor effluent. The large amount of isoparaffin which must accordingly be passed, unreacted, through the alkylation reactor and settler and separated from the alkylate product necessitates the use of fractionation equipment of large capacity in order to provide an adequate separation of the product alkylate from the isoparaffin to be recycled. Limitations on the amount of excess isoparaffin employed are primarily of an economic nature. The expense and difficulty of providing a large isoparaffin throughput and recycle may be obviated, in part, through the use of the process of this invention.
It is known that higher quality alkylate may be produced, in the alkylation of different molecular weight olefins such as propylene and butylenes, etc., with an isoparaffin, when one olefin, for example, propylene is separately alkylated with the isoparaffin at one set of reaction conditions while, for example, butylenes are alkylated with the isoparaffin at a different set of reaction conditions. However, it has been found necessary to maintain the same high molar excess of isoparaffin to olefin in both the propylene alkylation reaction and the butylenes alkylation reaction in order to provide an adequate product. The separate alkylation of, for example, C.sub.3 and C.sub.4 olefins has, therefore, been found uneconomical, because of the expense of providing separate reactors for the C.sub.3 and C.sub.4 olefins when combined with the above-noted expense and difficulties in handling the large molar excess of isoparaffin, to provide a high quality product.